Powder metallurgy has recently been the basis for the development of more efficient and versatile methods of manufacturing structural parts. In the production of metal powders for use in making these parts, it is often desirable to have additional metals on the surface of the base powder particles, so that upon pressing and sintering, desired alloys form along the grain boundaries. One art-recognized technique for accomplishing this result is to coat the particles with a sticky substance and then apply a dusting of the alloying metal ingredients. The core powder particles, coated with alloying metal ingredients, are then heated to produce diffusion-bonded alloy particles on the surface of the core particles. Such pretreated powders have been known to substantially improve the strength-elongation properties of the finished product. However, the application of the alloying metallic elements is not particularly uniform and this is known to influence properties.
Another technique for providing alloying ingredients is to form a melt of the base metal and alloying ingredients prior to powderization. This procedure produces a pre-alloyed powder of excellent uniformity, but such powders are hard and have less compressibility in the green state, and therefore lower density in the sintered state, than do powders that are not pre-alloyed.
While, as a whole, such techniques are indicative of the state of the art for providing alloying elements to metal particles for promoting physical properties, these efforts have not been concerned with particular problems associated with the current developments of powder metallurgy for maximizing structural integrity. Accordingly, there is a need for a procedure for manufacturing core metal particles with a chemically-uniform coating of a metal, an alloy or alloying ingredient, or a series of said coatings applied in a chosen sequence for the promotion of desired grain boundary properties of pressed and sintered products. In particular, there is a need for a highly compressible powder composition of base metal and alloying ingredients in uniform concentrations.